Anyway, why would someone need a big fat slug like a 777 to deliver a nuke? Filling it with conventional explosives and full of gas would do the trick, and a sports stadium full of people would make the perfect target.
Range. That plane, full up, has a range of thousands of miles.
Payload. Stripped down, the plane can a potentially huge payload - and primitive nukes are pretty heavy. A simple one, like “Little Boy” would weigh five tons or more.
Stealth - As someone pointed out, an airliner will only be shot down with great reluctance. They can use the passengers as hostages, to boot.
The 777 would make a great “intercontinental cruise missile.”